... by splitting the generated type definitions into separate files.

Currently all the generated GTypes for enumerated types were being
added to the thumbnailer, even though the thumbnailer didn't need them.

This was made worse by the fact that the enumerated types were defined
in header files that declared new GObject classes or functions. So,
when these header files were included to register the GTypes, it also
pulled in those other declarations in them.

!65